Photographic diffusion transfer process

ABSTRACT

PRESSURE DESENSITIZATION IN WHICH A SILVER HALIDE EMULSION IS SUBJECTED TO A PRESSURE OF 6-10 POUNDS PER LINEAR INCH IS AVOIDED BY EMPLOYING A SILVER HALIDE EMULSION CONTAINING A COLLOIDAL ALKALI PERMEABLE BINDING MATERIAL COMPRISING ABOUT 20 TO ABOUT 85% BY WEIGHT OF A SUBSTANTIALLY WATER INSOLUBLE POLYMER PREPARED FROM A MONOMERIC MIXTURE CONTAINING AT LEAST 50% BY WEIGHT OF ONE OR MORE ALKYL ACRYLATES HAVING AN ALKYL CHAIN OF 1 TO 10 CARBON ATOMS.

United States Patent 3,576,628 PHOTOGRAPHIC DIFFUSION TRANSFER PROCESS Dorothy J. Beavers, Rochester, N.Y., assignor to Eastman Kodak Company No Drawing. Filed Jan. 25, 1967, Ser. No. 611,592 Int. Cl. G03c 5/54 US. C]. 96-29 14 Claims ABSTRACT OF THE DISCLOSURE Pressure desensitization in which a silver halide emulsion is subjected to a pressure of 6-10 pounds per linear inch is avoided by employing a silver halide emulsion containing a colloidal alkali permeable binding material comprising about 20 to about 85% by weight of a substantially water insoluble polymer prepared from a monomeric mixture containing at least 50% by weight of one or more alkyl acrylates having an alkyl chain of 1 to 10 carbon atoms.

This invention relates to the photographic silver halide diffusion transfer process, more particularly to a method of reducing the effect of pressure on a silver halide emulsion.

According to the well known silver halide diffusion transfer process, a light sensitive silver halide emulsion layer is exposed imagewise and developed in contact with a specially prepared receiving layer in the presence of a solvent for silver halide. The exposed image areas are developed in the emulsion layer and the unexposed areas are dissolved by the solvent for silver halide which is present either in the developer or in the receiving layer. The solubilized silver halide is then transferred by diffusion to the receiving layer where it is physically developed into a visible image. The receiving layer contains development nuclei or a silver precipitating agent. The image formed in the receiving sheet is a positive image with respect to the image to which the emulsion layer has been exposed.

In one embodiment of the diffusion transfer system, the exposed emulsion layer is contacted against a receiving sheet which contains pods which are broken by passing through a roller mechanism. This results in causing the pod contents, a silver halide developer and/ or complexing agent, to be applied to the surface of the exposed emulsion. After a period of time, the receiving sheet and emulsion are separated with a positive image on the receiving sheet and the negative can be discarded. However, sufiicient pressure must be applied by the roller mechanism to crush or break the pods and this pressure may have an adverse effect on the emulsion. For instance, the emulsion may be desensitized where the greatest pressure is applied, resulting in failure of that area to reproduce or else resulting in lines which show where the pressure was applied.

In another embodiment, the sensitive film is contained in a film pack in which pressure is applied to the back of the film by a spring loaded device such as a plate, metal strips, etc. In this structure, the type of pressure may result in desensitization in the areas where pressure is applied when one sheet of the negative element is pulled past one or more sheets in the film pack.

Other sources of pressure desensitization include the mechanical equipment, particularly in the situation wherein a sheet of sensitized material held by vacuum means is passed over some hard particle or protrusion. Since pressure desensitization can be highly detrimental, it has been desirable to find a method of alleviating the effects of pressure.

I have discovered that by substituting all or part of the binder with a water insoluble alkyl acrylate polymer, that the pressure desensitization is substantially reduced. I

One object of this invention is to provide a photographic element for use in the diffusion transfer process being substantially free from desensitization due to pressure. Another object is to provide a method of preparing a silver halide emulsion which renders the emulsion resistant to pressure desensitization. An additional object is to provide alkali permeable colloid binders for silver halide emulsions which are suitable for use in the diffusion transfer system which are relatively free from pressure desensitization. A still further object is to provide a binder which can be mixed with gelatin resulting in a binder relatively free from pressure desensitization but which has satisfactory photographic properties.

The above objects are attained by using as a gelatin extender or substitute, at least one water insoluble alkyl acrylate polymer which contains at least 50% alkyl acrylate. The polymer is in a latex or hydrosol form and when mixed with gelatin, increases the flexibility and is compatible with photographic emulsions.

A particularly effective class of interpolymers or homopolymers useful for this purpose is prepared from acrylic type esters having active methylene groups in the ester moiety or in a substituent alpha to the carbonyl group. Such compounds can be represented by the formula:

0 OHz=C-(3OR2 1'1. where R is hydrogen, alkyl (1-10 carbon atoms) or R-O(3CH2X where R is alkylene (1-10 carbon atoms) and X is aliphatic acyl or cyano and R is alkyl (1-10 carbon atoms), cycloalkyl, aryl or R-O(3CH:X

where R and X are defined, provided that one and only one R and R is always The ethylenically unsaturated polymerizable monomers having the above formula can be prepared using any procedure suitable for this purpose. In general, the reaction of acid chlorides, acid anhydrides or mixed anhydrides containing active methylene groups with acrylic esters containing. hydroxyalkyl substituents can be employed. A preferred synthesis for preparing the esters having an active methylene group in the ester moiety involves the reaction of a hydroxyalkyl ester of acrylic or an alpha-alkyl acrylic acid with diketene or cyanoacetyl chloride. The esters having active methylene groups in the alpha-substituent in the above formula can be obtained by reacting the alpha-hydroxyalkyl substituted acrylic esters with diketene or cyanoacetyl chloride. Such reactions are not particularly pressure sensitive and, therefore, can be carried out at atmospheric, superatmospheric or subatmospheric pressure. The temperature range is subject to wide variation depending, for example, upon the particular reactants employed, solvents and like considerations, but generally temperatures up to about C. and often temperatures in the range of about 35 to about 100 C. are suitable. The reaction can be carried out in the absence of solvent or using a suitable vehicle, for example, diethyl ether, ethyl acetate or the like and is generally completed in less than 20 hours, often less than 4 hours. The acrylic esters containing the active methylene groups are generally viscous liquids or oils and can be separated from the reaction medium by any means suitable for this purpose, for example, by distillation.

The interpolymers employed in photographic materials according to the practice of this invention are filmforming, addition interpolymers containing at least about 0.1%, generally about 0.1 to about 1.4%, by weight, of active methylene groups in aliphatic side chains of the interpolymers. Active methylene groups are methylene groups between two activating groups, for.- example, electronegative groups such as carbonyl. Such methylene groups exhibit unusual chemical activity and are said to be active. Malonic esters, acetoacetic esters, cyanoacetic esters and 1,3-diketones are examples of compounds containing such groups. The active methylene groups are usually separated from the main polymer chain by at least three atoms and can be introduced into the side chains of an interpolymer by copolymerizing a monomer containing at least one active methylene group, for example, a

group, and an independently polymerizable unsaturated methylene group with at least one other copolymerizable monomer containing, for example, at least one -CH==C or CH =C group. Where reference is made to the fact that the active methylene groups are aliphatic side chains of the interpolymers, this is intended to mean that the chain which links the active methylene group to the main polymer chain of the interpolymer is free of non-aliphatic groups, e.g. aromatic groups, i.e. the active methylene group is bonded to the main chain or backbone of the interpolymer through an aliphatic linkage. The molecular weights of the interpolymers employed in photographic emulsions and elements according to the practice of this invention are subject to wide variation, but are often in the range of about 5000 to about 500,000.

A particularly useful class of polymers containing active methylene groups in aliphatic side chains and which can be employed as substitutes for gelatin in photographic emulsions and elements is prepared by interpolymerizing at least one unsaturated polymerizable compound containing one or more CH C groups with a dilferent monomer having the formula:

where R and R are as defined hereinbefore.

Useful gelatin substitutes include, therefore, interpolymers of acrylic monomers having the above formula with other ethylenically unsaturated polymerizable monomers which form addition polymers, such as vinyl esters, amides, nitriles, ketones, halides, ethers, alpha-beta-unsaturated acids or esters thereof, olefins, diolefins and the like, as exemplified by acrylonitrile, methacrylonitrile, styrene, alpha-methylstyrene, acrylamide, vinyl chloride, vinylidene chloride, methyl vinyl ketone, fumaric, maleic and itaconic esters, 2-chloroethyl vinyl ether, acrylic acid, methacrylic acid, dimethylaminoethyl rnethacrylate, 4,4,9 trimethyl '8 oxo 7 oxa 4 azonia-9-decenel-sulfonate, N vinylsuccinamide, N vinylphthalamide, N-vinylpyrazolidone, butadiene, isoprene, vinylidene chloride, ethylene and the like.

A preferred class of vinyl or addition interpolymers which can be employed as gelatin substitutes in photographic materials are interpolymers of (A) about 50 to about 90%, by weight, of a monomer (1) having the formula:

4 where R is hydrogen or methyl and R is alkyl, desirably containing up to about 10 carbon atoms, as exemplified by methyl, propyl, isobutyl, octyl, decyl and the like, (B) about 3 to about 20%, by weight, of a sulfoester monomer (2) having the formula:

where R is hydrogen or alkyl, desirably containing up to about 12 carbon atoms, often 1-8 carbon atoms, as exemplified by methyl, pentyl, octyl, dodecyl and the like, R has its valence bonds on different carbon atoms and can be a divalent hydrocarbon radical or divalent aliphatic hydrocarbon radical in which a chain of carbon atoms joining the oxygen and sulfur atoms in the above formula is interrupted by an atom from Group llV-A of the Periodic Table having an atomic weight of less than about 33, i.e. at least one --O- and/or S radical interrupts the carbon chains and M is a cation and (C) about 2 to about 20%, by weight, of a monomer (3) having the formula:

CH2=?- -O R5 R4 where R, is hydrogen, alkyl, desirably containing up to 12 carbon atoms as exemplified by methyl, n-butyloctyl,

methyl, butyl, octyl, decyl and the like, cycloalkyl, de-

sirably containing up to about 10 carbon atoms, as exemplified by cyclopentyl, cyclobutyl, cyclohexyl and the like, aryl, desirably containing up to about 12 carbon atoms, as exemplified by phenyl and the like or Ra0 -CH2X where R and X are as defined hereinabove for this radical, provided that one and only one of R and R is always O -RO( i-CH2X where R in the sulfoester monomer (2) above is hydrocarbon, it can be any aliphatic, cycloaliphatic or aromatic radical and will generally contain up to about '12 carbon atoms. Preferred hydrocarbon R radicals are alkylene radicals, generally those containing 2-4 carbons. R can also be a divalent aliphatic hydrocarbon radical in which there is a O- and/ or S radical and generally contains up to 12 carbon atoms. Such R radicals can, therefore, be saturated or unsaturated, although saturated divalent alkylene groups in which the carbon chain is interrupted by oxygen and sulfur atoms are preferred. Suitable R radicals include, for example, ethylene, 1,3-propylene, 1,2-propylene, tetramethylene, 1,3-isobutylene, pentamethylene, hexamethylene, octamethylene, phenylene, bisphenylylene, naphthylene, cyclopentylene, cyclohexylene, 2-butylene, butynylene, 2-oxatrimethylene, 3-thiapentamethylene, and the like. M in the sulfoester monomer (2) is a cation, as exemplified by hydrogen, an alkali metal such as sodium or potassium, ammonium, the cation of an organic amine such as triethylene amine, diethanol amine and the like.

Another class of vinyl or addition interpolymers which can be employed as gelatin substitutes in photographic materials are interpolymers in which acrylic acid is used in place of the sulfoester monomer (2). These interpolymers are film-forming, addition interpolymers of (A) about 50* to about 90%, by weight, of a monomer (1) having the formula:

where R and R are as defined hereinbefore for monomer (1), (B), about 3 to about 20%, by weight, of acrylic acid and (C) about 2 to about 20%, by Weight, of a monomer (3) having the formula:

where R; and R are as defined hereinbefore. The preferred class of interpolymers containing sulfoester units preferably contain, in polymerized form, at least about 65%, by weight, of monomer (1), at least about 3%, by weight, of sulfoester monomer (2) and at least 2%, by weight, of monomer (3). The preferred class of interpolymers containing acrylic acid units preferably contain, in polymerized form, at least about 65%, by weight, of monomer (1), at least about by weight, of acrylic acid and at least about 5%, by weight, of monomer (3). The temperature at which the interpolymers or homopolymers described herein are prepared is subject to wide variation since this temperature depends upon such variable features as the specific monomer used, duration of heating, pressure employed and like considerations. However, the polymerization temperature generally does not exceed about 110 C., and most often it is in the range of about 50 to about 100 C. The polymerization can be carried out in a suitable vehicle, for example, water or mixtures of water with water miscible solvents, as exemplified by methanol, ethanol, propanol, isopropyl, alcohol, butyl alcohol, and the like. The pressure employed in the polymerization, if any, is usually only sufiicient to maintain the reaction mixture in liquid form, although either superatmospheric or subatmospheric pressures can be used. The concentration of polymerizable monomer in the polymerization mixture can be varied widely with concentrations up to about 40% by Weight, and preferably about 20 to about 40% by weight, based on the weight of the vehicle, being satisfactory. Suitable catalysts for the polymerization reaction include, for example, the free radical catalysts, such as hydrogen peroxide, cumene hydroperoxide, water soluble azo type initiators and the like. In redox polymerization systems, the usual ingredients can be employed. If desired, the polymer can be isolated from the reaction vehicle by freezing, salting out, precipitation or any other procedure suitable for this purpose.

Included in the substantially insoluble alkyl acrylate polymers are those described in US. Pats. 2,768,080, 3,178,296 and 2,376,005. However, other substantially insoluble alkyl acrylate polymers are useful provided at least of the polymer is an alkyl acryl-ate having 1-10 carbon atoms in the alkyl group.

As indicated in US. Pat. 3,142,568, issued July 28, 1964, it is sometimes advantageous to include a surface active agent or compatible mixtures of such agents in the preparation of vinyl or addition polymers and in coating photographic materials containing such polymers. Suitable wetting agents include the non-ionic, ionic and amphoteric types as exemplified by the polyoxyalkylene derivatives, amphoteric amino acid dispersing agents, including sulfobetaines and the like. Such Wetting agents are disclosed in US. Pat. 2,600,831, issued June 17, 1952; US. Pat. 2,271,622, issued Feb. 3, 1942; U8. Pat. 2,271,623, issued Feb. 3, 1942; U.S. Pat. 2,275,727, issued Mar. 10, 1942 and US. Pat. 2,787,604, issued Apr. 2, 1957; US. Pat. 2,816,920, issued Dec. 17, 1957 and US. Pat. 2,739,- 891, issued Mar. 27, 1956. It has been found that a particular type of non-ionic wetting agent will give outstanding results when so employed. It is particularly convenient to use the non-ionic wetting agents described hereinafter in the formation of the interpolymers containing active methylene groups in their side chains and then incorporate the reaction mixture into a photographic emulsion or element. The wetting agents are generally employed in the polymer preparation in concentrations in the range of about 1% to about 5% based on polymerizable monomer and in coating photographic elements at concentrations in the range of about 0.1 to about 5 by weight, based on binding agent. Particularly suitable non-ionic wetting agents or coating aids are disclosed in Belgian Pat. 652,- 862 as having the formula:

CHzCHOHCHzO H TABLE I The above surface active materials, when incorporated in photographic hydrophilic colloid coating compositions and hydrophilic colloid coatings which can, but need not, contain photographic silver halide, increase the ease and efficiency of the coating process and provide a favorably high degree of surface roughness and excellent developer rewettability on coated layers having few or no repellencies, without adversely affecting the photographic properties of the final product. These coating aids are compatible with both acidand lime-processed gelatin as well as a wide variety of photographic emulsion addenda such as hardeners, antifoggants, mordants, couplers, antistatic agents, and the like.

Dispersions of the photographic silver halide containing the film-forming, addition interpolymers containing active methylene groups, in combination with photographic binding agents, such as gelatin, can be made in a variety of ways. For example, an aqueous gelatin dispersion of the photographic silver halide can be mixed with an aqueous dispersion or solution of the interpolymer. Alternatively, the photographic silver halide can be precipitated in an aqueous dispersion or solution of the interpolymer with or without another colloid, depending upon the dispersing characteristics of the interpolymer. In this case, a water soluble silver salt such as silver nitrate is admixed with a water soluble halide such as potassium bromide in the presence of the mixture. In still another procedure, the photographic silver halide is precipitated in an aqueous gelatin solution and digested in the conventional manner known to the art. After digestion, but prior to coating, there is added to the emulsion an aqueous dispersion of the interpolymer containing active methylene groups in its side chains. The bulk of the resulting dispersion can be increased by the addition of more of the interpolymer and/or natural or synthetic colloids or other binding agents suitable for use in photographic silver halide emulsions. Satisfactory colloids include, for example, gelatin, protein derivatives e.g. carboxy methylated proteins, colloidal albumin, cellulose derivatives, synthetic resins such as polyvinyl compounds, e.g. polyacrylamide and the like.

The gelatin substitutes described herein can be employed as the binding agent in one or more layers of a photographic silver halide element. However, photographic silver halides are generally precipitated in the presence of binding agents such as gelatin or other colloids which exhibit very good peptizing action. Therefore, the photographic silver halide emulsions or layers of this invention will generally contain some binding agent such as gelatin which exhibits this very good peptizing action. Generally, the concentration of the interpolymers described herein will be in the range of about 20 to about 85 often in the range of about 50 to about 85%, by weight, based on total binding agent (dry weight), employed in photographic emulsions, photographic emulsion layers or other layers of a photographic element. In the preferred case, the remainder of the binding agent is gelatin, although other colloids also give good results. The silver halide employed in the preparation of light sensitive coatings described herein includes any of the photographic silver halides as exemplified by silver bromide, silver chloride and silver iodide, or mixed silver halides such as silver chlorobromide, silver bromoiodide, and the like. Very good results are obtained with high contrast silver halide emulsions in which the halide comprises at least 50 mole percent chloride. Preferred emulsions of this type contain at least 60 mole percent chloride; less than 40 mole percent bromide and less than mole percent iodide.

The photographic compositions described herein can be coated on a wide variety of supports. Typical supports include polymeric films such as cellulose acetate film, polyvinyl acetal film, polystyrene film, polypropylene film and other polyolefin film, polycarbonate film, polyethylene terephthalate film and other polyester film as well as glass, paper, wood and the like. Supports such as paper which are coated with alpha-olefin polymers, particularly polymers of alpha-olefins containing 2-10 carbon atoms, as exemplified by polyethylene, polypropylene, ethylenebutene copolymers and the like give good results.

The emulsions containing the interpolymers can be chemically sensitized with compounds of the sulfur group, noble metal salts such as gold salts, reduction sensitized with reducing agents, and combinations of these. Furthermore, emulsion layers and other layers present in photographic elements made accorling to this invention can be hardened with any suitable hardener such as aldehyde hardeners, such as formaldehyde, mucochloric acid and the like, aziridine hardeners, hardeners which are derivatives of dioxane, oxypolysaccharides such as oxystarch, oxy plant gums and the like. Such hardened layers will have a melting point in water greater than about 150 F. and preferably greater than 200 F.

The emulsion can also contain additional additives, particularly those known to be beneficial in photographic emulsions, including for example, stabilizers or antifoggants, particularly the water soluble inorganic acid salts of cadmium, cobalt, manganese and zinc as disclosed in U.S. Pat. 2,829,404, the substituted triazaindolizines as disclosed in U.S. Pats. 2,444,605 and 2,444,607, speed increasing materials, absorbing dyes, plasticizers and the like. Sensitizers which give particularly good results in the photographic compositions disclosed herein are the alkylene oxide polymers which can be employed alone or in combination with other materials, such as quaternary ammonium salts, as disclosed in U.S. Pat. 2,886,437 or with mercury compounds and nitrogen containing compounds as disclosed in U.S. Pat. 2,751,299.

EXAMPLE I A coarse-grained silver bromoiodide emulsion was coated on a paper support at 145 mg. Ag/ft. and 320 mg. of gelatin/ft. as the control (51). In subsequent coatings, the gelatin level was reduced to 200 mg./ft. and the following synthetic vehicles added in an amount of 200 mg./ft. Mg./ft. 55 Polymer 1* 200 59 Polymer 2* 200 63 Polymer 3* 200 The following additional coatings were made like those above except that a gelatin layer (overcoat) was coated over the emulsion layer at 100 mg. of gelatin/fe the type and concentration of synthetic vehicle which was used as above with 200 mg./ft. of gelatin is as follows:

52 Like control above (51). Mg./ft. 54 Polymer 1* 67 56 Polymer 1* 200 58 Polymer 2* 67 64 Polymer 3* 200 *Polymer identification 1 N-butyl acry1ate-10% acrylic acid copolymer; de- %cr1b1ed in U.S. Pat. 3,287,289 in the names of Beam and ow er.

2. Methyl acrylate-sulfopropyl acrylate-2-acetoacetoxyethyl methacrylate copolymer as described in Example 10 of U.S. Pat. No. 3,459,790 issued Aug. 5, 31969 to Donald A. Smith.

3. butyl acrylate-5% sulfopropyl acrylate copolyrner as described in U.S. Pat. No. 3,459,790.

4. Copo1y(butyl acrylate-sulfopropyl acrylate-2-acetoxyethyl methacrylate) as described in U.S. Pat. N0. 3,459,790.

TESTING These negative film coatings were exposed and tested and contacted against a receiving sheet prepared as follows:

follows:

A dispersion of colloidal palladium nuclei-in an alkyl acrylate acrylic acid polymer latex was coated on a polyethylene coated paper support to give a nuclei level of 0.035 mg./ft. and 39 mg./ft. solids.

1 Almost invisible. *See notes for polymer identification.

In addition to reduction of pressure sensitization in the medium density areas, the coatings containing synthetic vehicles showed less difference between the background and pressure mark in the D area as compared to the all-gelatin controls.

Pressure sensitivity was measured as the length and density of the line resulting on the positive transfer as compared to the adjacent area in the unpressurized negative. The pressure was obtained by pulling a negative face up against a similar negative underneath with an H bar Weighing 500 g. on the face of the test negative. Each of the two legs of the H resting on the test negative were A of an inch wide giving a pressure of about 8.8 pounds per linear inch. From a fiducial midway on the sensitometric scale in the medium density area of the transferred print, pressure marks on the number of steps into the toe were observed. D in all coatings was 0.01-0.02.

The test strips were exposed through a step tablet having twenty-two steps and the midway mark (fiducial) used arbitrarily as a guide to determine the point from which the number of steps was designated to show the extent of the pressure desensitization. For instance, in the control, 40 the emulsion was desensitized in the pressure areas as was apparent through five steps. In one improved coating, the desensitization was reduced so that it was only evident in three steps past the midway mark.

EXAMPLE II A coarse-grained silver bromoiodide emulsion was coated on a paper support at 145 mg. Ag/ft. and 320 mg.

of gelatin/ft. as the control (10) In subsequent coatings, the gelatin level was 200 mg./ft. and the following synthetic vehicles added to the 200 mg./ft. of gelatin:

Mg./f-t. 12 Polymer 3* 200 13 Polymer 4* 200 14 Polymer 2* 200 Pressure sensitivity Synthetic vehicle Coating Number (g./m.) Dina; Steps Density 10 1.20 3+ Grey. 12 Polymer 3* (150)-. 1.14 2+ Lt. grey.

...- Polymer 4* (150).. 1. 24 1+ Do. Polymer 2* (150)-. 1. 14 3 V. lt. grey *See notes for polymer identification.

at least 6-12 pounds per linear inch.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as defined hereinabove and as defined in the appended claims.

I claim:

1. In a diffusion transfer process in which a silver halide emulsion is subjected to a pressure of 6-10 pounds per linear inch during processing, the improvement wherein the silver halide emulsion contains a colloidal alkali permeable binding material comprising about 20 to about by weight of a substantially water insoluble polymer having a molecular Weight of about 5,000 to about 500,- 000 prepared from a monomeric mixture containing at least 50% by weight of one or more alkyl acrylates having an alkyl chain of 1 to 10 carbon atoms and 5 to 50% by weight of a monomer selected from the class consisting of sulfo alkyl acrylates, acrylic acids and butoxy alkyl acrylates.

2. A process of claim 1 in which the said alkyl acrylate is represented by the structure:

CHz=$%-OR2 wherein R is hydrogen, alkyl or o RO( i1CHrX where R is alkylene and X is aliphatic, acyl or cyano and R is alkyl, cycloalkyl, aryl or o -RO(IB'CH2X where R and X are as defined above.

3. A process of claim 1 in which the alkyl acrylate is polymerized 'with a polymerizable compound containing at least one CH =C group.

4. A process of claim 1 in which the said binding material contains gelatin.

5. A process of claim 1 in which the said polymer is an interpolymer of about 50 to about by weight of a monomer having the formula:

where R is hydrogen or methyl and R is alkyl.

6. A process of claim 1 in 'which the said polymer is an interpolymer of about 3 to about 20% by weight of a sulfoester monomer having the formula:

where R is hydrogen or alkyl, R, has its valence bonds on different carbon atoms and M is a cation.

7. A process of claim 1 in which said polymer is an interpolymer of about 3 to about 20% by weight of acrylic acid.

8. A process of claim 1 in which the said emulsion contains at least one surface active agent.

9. In a process of claim 1 the improvement comprising the use of a silver halide emulsion containing as a portion of said binding mlterial a substantially water insoluble polymer prepared from a monomer mixture containing at least 50% by weight of alkyl acrylate having the formula:

1 1 wherein R is hydrogen, alkyl or where R is alkylene, and X is aliphatic, acyl or cyano and R is alkyl, cycloalkyl, aryl or where R and X are defined above, the amount of said polymer being 20-85% by weight, :based on the total weight of binder.

10. A process of claim 1 in which the said emulsion contains a silver halide developing agent.

11. A process of claim 1 in which the said polymer is a copolymer of about 90% n-butyl acrylate and about 10% acrylic acid.

12. A process of claim 1 in which the said polymer is a methyl acrylate-sulfopropyl acrylate 2 acetoacetoxy ethyl methacrylate copolymer.

13. A process of claim 1 in which the said polymer is a copolymer of about 95% butyl acrylate and about 5% sulfopropyl acrylate.

3,411,911 11/1968 Dykstra 96114 3,396,018 8/1968 Beavers et a1 9629 FOREIGN PATENTS I 900,195 7/1962 Great Britain 96-114 7 OTHER REFERENCES- A. J. Reardon, Jinl. Op. Soc. Am., 29 (10), 1939 pp.

S. P. Choong, Jinl. Op. Soc. Am., 34 (5), 1944 pp. 285-289.

NORMAN G. TORCHIN, Primary Examiner J. L. GOODROW, Assistant Examiner US. 01. X.R. 

